This three year, competing continuation application consists of two interrelated parts. The first part will continue a longitudinal study of the relationships between risky behavior; engagement/non-engagement in treatment; psychiatric symptoms; infection with HIV, HTLV I and II; and disease progression among IDU's who are both in-treatment (IT) and out-of- treatment (OT). This part is a continuation of a study that was previously funded by MDA, and which has recently been expanded by supplemental funding from NIAID and NIDA in preparation for clinical trials of preventative HIV vaccines. The supplemental funding allows us to increase the sample size and the frequency of psychological, behavioral and serological assessments from every 6 to every 3 months for both IT and OT subjects who are seronegative. The second part will be a study of three brief interventions, delivered at each of four post-test counseling sessions over a period of one year. 270 subjects, half male and half female, half IT and half OT, who agree to participate will be randomly assigned to one of the three interventions: standard post-test counseling alone; counseling plus a computer-assisted risk assessment that provides immediate feedback on specific areas in need of risk reduction; or counseling plus an intervention that combines an assessment of readiness for behavioral change with a brief therapy that focuses on achieving change in the context of specific relationships within the person's social network. Based on our experience to this point, we feel that, particularly for the OT subjects, these brief interventions may be among the only opportunities intervene toward reducing their HIV risk behaviors. The computer-assisted feedback and the therapy intervention will be delivered every three months for one year. Followup will include the standard evaluations that are part of our ongoing study. These are: serologic testing for HIV, HTLV I and Il; and behavioral and psychiatric assessments. Testing for syphilis and herpes will be added to the assessment battery. Followup will occur at each three month assessment throughout the study and continue quarterly over the following year. Subjects who become seropositive will continue in their assigned treatment condition, and will continue to have behavioral and psychiatric assessments done every three months. These data will be analyzed to assess for differences in both drug and sex behavioral risk reduction, engagement and retention in treatment, as well as HIV and STD conversion rates among the three intervention groups and as a function of gender and IT vs. OT status across these interventions. This project builds upon our success in engaging and maintaining longitudinal cohorts of IDU's, the high followup rates achieved for delivering post-test counseling, our previous experience in studying treatment interventions, and an opportunity that has been presented by the vaccine initiative for increased behavioral, psychological, and serological assessments.